Many commercial cellular handsets require multi-band operation. Typically, a 2G/3G cellular transceiver may cover a number of 2G frequency bands (e.g., 850, 900, 1800, and 1900 MHz) and several 3G frequency bands (e.g., bands I, II, III). The existing multi-band approach may be inefficient in term of cost and area. The limitation of such multi-band approach may stem from the need for highly selective radio-frequency (RF) filters, such as SAW filters for 2G and duplexers for 3G operation. With the introduction of new technologies such as 4G and multiple antennas, and the demand to cover more frequency bands, the number of required RF filters and duplexers may increase to an impractical level, in terms of cost and area.
An optimal implementation of a multi-band transceiver may include an antenna-ready radio, completely integrated on a single CMOS chip. The single chip solution may have a performance advantage of saving on the RF switch and printed circuit board (PCB) loss. One of the missing pieces to realize the single CMOS chip antenna-ready radio is a wideband multi-band RF duplexer, for example, a wideband integrated RF duplexer supporting 3G/4G (e.g., supporting bands, such as bands I, II, III, IV, and IX). The RF duplexer may provide isolation in transmit (TX) band to avoid saturation of the receiver, and also to relax the linearity and phase noise requirement of the receive (RX) path. In a conventional duplexer, isolation is achieved using frequency-selective filters (e.g., surface acoustic wave (SAW) filters). However, SAW filters cannot be integrated on a silicon-based chip. Further, a SAW filter typically has a narrow bandwidth, as a result, a conventional duplexer operating in multiple frequency bands may require multiple SAW filters (e.g., one for each frequency band), increasing the size and cost of the RF board.
Therefore, the need exists for a low cost, small size, and wideband RF duplexer circuit.